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Microsoft has confirmed reports that several versions of Windows are vulnerable to exploits that allow remote attackers to take full control of users' computers using booby-trapped emails and websites.

In an advisory issued Tuesday, Microsoft said it was investigating “new public reports” of vulnerability in the XP, Server 2003, Vista, and Server 2008 versions of Windows. In fact, the first known report of the bug in the way those operating systems process thumbnail images came on December 15 at a security conference in South Korea. On Tuesday, exploit code was added to the Metasploit software framework for hackers.

“This is a remote code execution vulnerability,” the Microsoft advisory stated. “An attacker who successfully exploited this vulnerability could take complete control of an affected system.”

The flaw resides in the Windows Graphics Rendering Engine and can be exploited when victims view a specially manipulated thumbnails on network-shared folders or drives or in online WebDAV-shared folders. It can also be targeted when email users open or preview Microsoft Word or PowerPoint files that contain the doctored images.

There are no known reports of attacks in the wild that exploit the vulnerability, and Windows 7 and Server 2008 R2 aren't susceptible.

“The vulnerability is exploited by setting the number of color indexes in the color table to a negative number,” Johannes Ullrich, chief research officer at the Sans Institute, blogged. Slides from the December 15 conference provide hints that the exploits can bypass security measures such as data execution prevention and safe exception handling, he added.

In a blog post, Microsoft Senior Marketing Communications Manager for Trustworthy Computing, Angela Gunn, said Microsoft was working on a patch, but that for the time being “the circumstances around the issue do not currently meet the criteria for an out-of-band release.” Microsoft's next patch release is scheduled for January 11, but it's highly unlikely a bug fix will be ready by then.

Workarounds include configuring Windows Access Control List to be more restrictive, which will interfere with the way the Graphics Rendering Engine displays media files.

The bug is at least the third unpatched vulnerability in a piece of Microsoft software. Two weeks ago, the company warned of a vulnerability in Internet Explorer that creates a means for hackers to inject malware onto vulnerable systems. On New Year's Day, security researcher Michal Zalewski disclosed a separate bug in the Microsoft browser that he believes also allows attackers to hijack user PCs. ®